RISC vs. CISC – Decoding How RISC Architecture is Different from the CISC Architecture?

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In computer architecture, two significant instruction set designs have dominated microprocessor engineering: RISC (Reduced Instruction Set Computing) and CISC (Complex Instruction Set Computing). These architectures elaborate on the design and implementation of a processor’s instruction set, which impacts efficiency, performance, and overall system configuration.

CISC architecture has prevailed for decades, especially in personal computer systems and servers. However, in recent years, there has been a shift from RISC architecture to CISC architecture because they use more complex sets of instructions capable of executing multiple operations with a single instruction. Explore the comparison between RISC architecture vs CISC architecture in this blog. Also, navigate how RISC architecture differs from the CISC processors, along with the advantages of migrating from RISC to CISC processors.

Before diving deep into this blog, here is a summary of RISC vs CISC processor.

Understanding the Fundamentals of Computer Architecture

Nearly all the latest CPUs have different architecture designs to work from “Instruction Set Architecture.” Primarily, there are two types of architectural designs:

• RISC (Reduced Instruction Set Computing) Processors
• CISC (Complex Instruction Set Computing) Processors

These two designs differ in multiple ways. RISC architecture mainly focuses on executing commands while aiding some microprocessor cycles per command for optimum performance, while CISC architecture can perform multiple operations with a single set of instructions.

Also, it has diverse ways of addressing modes to access memory, which depends on the CPU framework, which requires a single set of instructions to carry out many low-level actions.

Understanding RISC Architecture

Reduced Instruction Set Computing, or RISC, is the CPU architecture designed to follow simple instructions. In simple terms, every command will perform small and simple tasks at a fast speed. Here, most instructions are of similar length as they divide all the complex instructions into a simple set of instructions through a process known as Pipelining.

What is Pipelining in RISC Microprocessor?

Pipelining is a multi-stage procedure that carries out single instructions in one machine cycle to increase the speed of RISC microprocessors. RISC uses a small set of instructions, so the number of chips used for transistors is small.

In RISC architecture, minimum decoding is required as the data types available in the hardware are fewer. The register needed for general purposes is common to all, while the addressing nodes are simple, and the instruction set is uniform. As a result, when a task is executed, RISC preserves the number of cycles it is carried out by eliminating the code’s unnecessary parts.

What are the Characteristics of RISC Architecture?

Here are some characteristics of RISC architecture:

• Simple set of commands that can be easily decoded and implemented.
• The size of the instruction set is very small, sometimes as small as a single word.
• It is a fast procedure as a single instruction is executed with just a single instruction.
• The general-purpose register quantity is larger.
• The variable data type is less in number.
• The addressing modes are quite simple.
• Achieving pipeline is the primary goal.

What are the Advantages of RISC Microprocessors?

Here are some of the advantages of using RISC microprocessors in the CPU design:

• Usage of Simple Instruction Sets: The simple set of instructions used in RISC processors makes them easy to decode and execute, resulting in faster processing. This way, it highlights the advantages of RISC over CISC in terms of speed.
• Reduced Power Consumption: The RISC processors consume less power, making them ideal for portable devices.
• Faster Output: The RISC microprocessor produces quicker results due to more uncomplicated instructions.

What are the Disadvantages of RISC Processors?

Here are some of the disadvantages of RISC processors:

• Increased Instructions-Sets Requirements: Many sets are required for instructions to perform complex tasks.
• Memory Usage: To store additional instructions for executing complex tasks, ample memory storage is needed.
• Expensive: The RISC processors are costly to design and manufacture.

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Understanding CISC Architecture

Complex Instruction Set Computing, or CISC architecture, is used to execute complex tasks with just a single command. It contains instructions for multiple steps required in an operation for execution in a program. Therefore, CISC architecture has comparatively smaller programs, while the size of their instruction set is large and requires quite some time to produce output.

In CISC architecture, various measures are taken to secure every instruction set, which means an extra set of commands for each instruction, which prolongs the output result. Depending on the instruction size, the instruction may take two or more machine cycles. Moreover, it doesn’t use the pipelining process as RISC architectures.

Key Features of CISC Architecture

Here are some noteworthy features of CISC architecture in CPU frameworks:

• CISC processor can quickly execute compound command output with a single complex set of instructions
• It can be used for compilers.
• It has a wide range of addressing nodes.
• CISC uses multiple data types for its machine hardware and can carry out processes for a low-level command.
• It is complex in nature.

What are the Characteristics of CISC Architecture?

Here are some characteristics of CISC architecture:

• It has a complex set of instructions; therefore, it is also known as decoding.
• The size of the instruction set is significant due to its complexity, which is often more than one word.
• The time taken to execute compound instruction is more than a single clock cycle.
• The number of general-purpose registers used is smaller as most operations are carried out in memory.
• Multiple data types are used in CISC microprocessors.
• The addressing mode framework is generally complex.

What are the Advantages of CISC Microprocessors?

Here are some of the advantages of using CISC microprocessors in the CPU design:

• Popularity: CISC microprocessors are widely used in software and have a more extensive user base.
• Code Size: It is a reduced code size as it uses complex instructions to execute multiple operations for a program.
• Memory-Effective Code: The instruction set of CISC architecture is more complex, requiring fewer commands for a program, making it more memory-efficient code.

What are the Disadvantages of CISC Processors?

Here are some of the disadvantages of CISC processors:

• Slow Execution Process: Due to the complexity of CISC architectures’ instruction sets, it takes longer to decode and execute the commands.
• Higher Power Consumption: Due to the complexity of their instruction sets, CISC processors require more power than other CPU frameworks like RISC architectures.
• Design Complexity: The design and manufacturing of CISC processors are complex, making production difficult.

RISC vs CISC Processor: Analyzing & Assessing the CPU Performance

Here is a brief analysis how the RISC vs CISC processor approaches enhance CPU performance.

• In RISC architecture, the number of clock cycles for each instruction is reduced at the cost of the total instruction per program.
• In contrast, in CISC architecture, the number of instructions sets used per program is reduced, but this increases the overall number of cycles per instruction.

RISC microprocessor is more popular for high-level language dependency as it uses simpler and faster instructions. However, when a task or programming is performed in assembly language, instructions are needed to carry out many tasks, as executing a program in assembly can be very tedious and prone to error. Due to this, the CISC architecture framework was developed to aid assembly programs.

For Example:

A task for the addition of two 8-bit numbers

1. RISC Architecture Approach:

• The programmer must create a load command to load the information in registers.
• For the next step, a suitable operator is required
• Finally, the output will be stored in the designated location.

Here, in the task of performing addition, the program is divided into three parts, i.e., load, operate, and store, which makes RISC programs long and requires more memory to store instructions while needing fewer transistors as the commands are simple and less complex.

2. CISC Architecture Approach:

• The task will be carried out with a single instruction or a command, ADD.

RISC vs CISC Architecture: A Comparative Analysis

Here is an in-depth comparison of CISC vs RISC architectures:

Can Stromasys Help with RISC Migration?

Aging legacy systems are mostly developed using RISC architecture, which lacks flexibility, scalability, and the ability to carry out complex instructions. Stromasys offers cross-platform emulation and virtualization solutions to migrate from outdated legacy applications to a modern platform like x86 systems or the cloud.

The x86 servers have a CISC-based architecture, which ensures they can easily interact with other solutions and perform complex tasks. Stromasys Charon emulation solutions create an interface similar to the original legacy hardware on a newer platform like, x86, so all the previous legacy applications run more efficiently.

Is your business also relying on the outdated legacy system with RISC architecture? Then, you are at the right stop. The Stromasys experts will assist you in the RISC migration of your aging legacy. They will help you with all your questions and problems regarding RISC processors and aging legacy hardware.

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Final Thoughts

Which microprocessor is more efficient, CISC vs. RISC architecture? It is debatable as each approach has its own strengths and weaknesses, while the evolution of technology is diminishing the lines between them. Businesses relying heavily on legacy systems are migrating to modern platforms to meet the ever-growing demands. While RISC architecture has been offering great assistance with its simple and fast instruction, with the evolving technologies, complex instruction is required, which makes CISC architecture a better candidate for performing a task. The future of processor design lies in finding the right balance between simplicity and complexity, power efficiency and performance, and cost-effectiveness.

Frequently Answered Questions (FAQs)

1. What are the CISC and RISC architectures called?

RISC (Reduced Instruction Set Computing) and CISC (Complex Instruction Set Computing).

2. What are the examples of RISC architecture-based legacy systems?

Here are some examples of legacy systems that are based on RISC architectures:

• DEC Alpha
• PA-RISC
• SPARC

3. Is the x86 server based on CISC architecture?

Yes, the design of the x86 server is based on CISC architecture.

4. Explain in brief about RISC processors.

RISC processors provide fast execution with simple individual instruction and effective pipelining.

5. What are the format ranges for RISC and CISC processors?

RISC processors use 32-bit fixed format, which is mostly register-based instructions, while CISC processors use variable format, ranging from 16 to 64 bits per instruction.

6. In terms of hardware complexity, how do RISC architecture vs CISC architectures compare?

When we compare CISC vs RISC architectures, CISC hardware is often more complex to support its wider range of instruction types and addressing modes, whereas RISC hardware tends to be simpler due to its reduced instruction set.

7. In terms of power efficiency, how do CISC vs. RISC processors compare?

RISC processors are often more power-efficient due to their simpler design and instruction execution, making them popular in mobile and embedded devices.

8. Code size comparison between RISC vs. CISC microprocessors?

Due to complex instructions, CISC microprocessors have a smaller code size, while RISC may require more instructions and thus result in a larger code size for the same functionality.